Technical Field
The present invention concerns a method of feeding electric power into an electric network, in particular using one or more wind power installations. The invention further concerns a wind power installation as well as a wind park and also a wind park arrangement with a plurality of wind parks.
Description of the Related Art
Methods of feeding electric power, in particular by means of wind power installations, into an electric network, are generally known. In addition to purely feeding the available energy or power when a snapshot is considered into the network, such methods for feeding power into the network can and often have to also take into account functions involving networks stabilization. Expressed in simplified terms, it can be provided that, in dependence on the voltage in the network to be fed into, hereinafter referred to for simplicity as the network, more or less power and/or more or less reactive power is to be fed in, to give just some examples. The network voltage, that is to say the amplitude of the electric voltage in the network, in particular an effective value of that voltage, can be an important parameter to implement in dependence thereon the network stabilization measures.
For example, international application WO 02/086315 A1 discloses a network voltage-dependent phase angle regulation and thus a voltage-dependent feed of reactive power. The German patent application laid open as laid-open application DE 19 756 777 A1 discloses a network voltage-dependent power regulation which alters the fed-in power in dependence on the network voltage.
By virtue of the wide dissemination of decentral feed-in apparatuses like wind power installations or wind parks with a plurality of wind power installations, the problem which arises is that a number of installations wish to implement network support independently of each other, in accordance with the same specification. That can have the effect that an installation seeks to compensate for the achieved effect of providing support by another installation. The problem occurs in particular when parameters in the network, in particular the network voltage, are subject to slight fluctuations, that is to say in particular fluctuate somewhat in amplitude and by coincidence one of the installations performing the test by way of example rather detects a lower value in respect of the voltage fluctuations and another installation performs a test and detects a higher value in respect of the fluctuations. In that case the installation which detects a value that tends to be lower is inclined towards initiating measures for increasing the voltage whereas the installation which tends to detect a higher value is inclined towards initiating measures for reducing the voltage. In that way the wind power installations coming on line can operate against each other. The situation can occur in which some network support operations are effected only by one installation, and the other installation makes little or no contribution. Since the voltage may fluctuate at different times and at different locations, this is a different problem.
In a wind park that problem can be resolved by the wind power installations being centrally controlled insofar as they receive for example a percentage adjustment value which is predetermined by a central control unit which correspondingly also operates only one voltage measurement process in the network. At any event the installations in such a wind park can no longer operate in opposition to each other as a result. Central park regulation is shown for example in European patent application EP 2 113 980 A2.
The above-mentioned problem that feeding installations can operate in opposition to each other or at least unwanted unequal distribution of network support occurs, can also correspondingly occur for a plurality of wind parks which are to feed into a network independently of each other. In a situation involving a plurality of different wind parks the problem also often arises that wind power installations from different manufacturers are respectively combined. That causes difficulty at least in coordination and joint presetting of target values, as was explained above for a plurality of wind power installations within a park.
As general state of the art attention is directed to US 2004/0010350, WO 2011/073670 A2 and WO 2009/068034 A1.